Here’s a little DIY project, great for kids and Scouts. You’re a climber, so that means you have a masochistic streak already, right? Here's the next logical step.
Cut about 5 meters of blackberry vines. Extra points for big scary thorns like the one below.
Go try to find a climbing book from the 1950s, where people tied harnesses out of hemp rope. Using one of those diagrams, braid the blackberry vines together. Notice, leather welding gloves strongly recommended.
When it's done, smear some mud on it and let it dry, so it all stays together.